00:00Ancient Roman piers still stand.
00:02Why haven't they crumbled?
00:04Textbooks get it wrong.
00:06Their concrete heals itself under water.
00:09Volcanic ash was their secret.
00:11It makes tiny crystals grow.
00:13Ocean water feeds these crystals.
00:15The concrete grows harder and stronger.
00:18This Roman concrete self-healed
00:21and strengthened under water.
00:23Discover more ancient engineering at the link in bio.
